Fix JSONStore and add MemoryStore option in Installation Docs

[thomasloux]

Summary

Fix the installation JSONStore (init requires paths and not uri). Also add MemoryStore in order to quickly test the installation as JSONStore does not work with all workflows (failing with PhononMaker with TypeError: Type is not JSON serializable: ScalarFloat).

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[JaGeo]

@thomasloux Thank you! I kind of forgot that this is still part of the Installation instructions!

I think we should suggest the MemoryStore as a default. Actually, it should work without the setup as well.

Would you mind changing this as part of this PR?

[thomasloux]

Indeed it works without setting anything (don't provide jobflow.yaml).

Do you want MemoryStore as default before MongoStore or just before JSONStore ?

[JaGeo]

@thomasloux just before JSONStore.

MongoStore is still the better option if you want to run high-throughput. We have been working on this as well to provide a different option.

[JaGeo]

@thomasloux Thanks!

If you want to, you can add yourself to the list of contributors in your second PR!